The present invention relates to improved continuous multifilament nylon apparel yarns and more particularly relates to a warp-draw process for making nylon flat yarns and improved yarn products made thereby.
Nylon flat yarns are used in a variety of woven and warp knit fabrics which are dyed before use. When small molecule dyes are used for these fabrics, uniform dyeing can usually be achieved without great difficulty. However, for some critical dye applications such as fabrics for swimwear and auto upholstery which require excellent wash and/or light fastness, it is desirable to use large molecule acid dyes. In dyeing these fabrics with large molecule acid dyes, even a small amount of non-uniformity in dye uptake of the flat yarns can result in highly-visible non-uniformity in fabric dyeing and thus poor fabric appearance.
Nylon flat yarns generally have break elongations of less than about 60% and thus may be referred to as "fully drawn" yarns. Typically, the high degree of orientation in known flat yarns is imparted by drawing during yarn manufacture in an integrated spin-draw process (speed of withdrawal from the spinneret of between about 1400 and 200 meters per minute (mpm) and wind-up speeds of between about 2500 and 3500 mpm) or in a split process in which a package of yarn spun at a withdrawal speeds of typically less than 1000 mpm is drawn in a separate process using a single-end draw winder. However, the yarns so produced have often been found to be undesirable for critical dye applications such as swimwear or auto upholstery due to the great care that must be taken during the preparation of such yarns and during the preparation and dyeing of the resulting fabrics to achieve acceptable dye uniformity.
Equipment has been sold which is capable of drawing of a warp of nylon yarns in a hot water bath. However, while processes using this equipment can increase dye uniformity, the equipment is recognized to have a number of inherent disadvantages. Processes using the equipment are messy and produce a waste stream of polluted water since the yarn finish is removed into water during drawing. Moreover, for use of the yarn in knitting, a finish must be reapplied after drawing. Another serious drawback of equipment which has been sold for wet drawing is that the speed of the process is typically limited to approximately 300-350 mpm by the limited capacity of the equipment to dry the yarns before wind-up.